In response to the demands of consumers who are driven both by ever-escalating fuel prices and the dire consequences of global warming, the automobile industry is slowly starting to embrace the need for ultra-low emission, high efficiency cars. While some within the industry are attempting to achieve these goals by engineering more efficient internal combustion engines, others are incorporating hybrid or all-electric drive trains into their vehicle line-ups. To meet consumer expectations, however, the automobile industry must not only achieve a greener drive train, but must do so while maintaining reasonable levels of performance, range, reliability, safety and cost.
The most common approach to achieving a low emission, high efficiency car is through the use of a hybrid drive train in which an internal combustion engine (ICE) is combined with one or more electric motors. While hybrid vehicles provide improved gas mileage and lower vehicle emissions than a conventional ICE-based vehicle, due to their inclusion of an internal combustion engine they still emit harmful pollution, albeit at a reduced level compared to a conventional vehicle. Additionally, due to the inclusion of both an internal combustion engine and an electric motor(s) with its accompanying battery pack, the drive train of a hybrid vehicle is typically more complex than that of either a conventional ICE-based vehicle or an all-electric vehicle, resulting in increased cost and weight. Accordingly, several vehicle manufacturers are designing vehicles that only utilize an electric motor, or multiple electric motors, thereby eliminating one source of pollution while significantly reducing drive train complexity.
In order to achieve the desired levels of performance and reliability in an electric vehicle, it is critical that the temperature of the traction motor remains within its specified operating range regardless of ambient conditions or how hard the vehicle is being driven. A variety of approaches have been used to try and adequately cool the motor in an electric car. For example, U.S. Pat. No. 6,954,010 discloses a device such as a motor, transformer or inductor that utilizes a stack of laminations, where a plurality of at least partially coincident apertures pass through the stack of laminations and define a plurality of coolant passageways. Manifold members located at opposite ends of the lamination stack are used to couple the coolant passageways to a suitable coolant pump and heat sink. A variety of aperture designs are disclosed, including both same-sized apertures that form straight passageways, and apertures that vary in size, shape and/or position to form non-axial passageways.
U.S. Pat. No. 7,633,194 discloses a system for cooling the stator lamination stack of an electric motor. The outer periphery of each of the laminations is defined by an array of outwardly projecting pins. A cooling jacket surrounds the stack. The outwardly projecting pins cooperate with the jacket to form a cooling space through which coolant flows.
U.S. Pat. No. 7,009,317 discloses a motor cooling system that utilizes a cooling jacket. The inner surface of the cooling jacket, which may form an interference fit with the stator, includes a series of grooves. The grooves along with the outer surface of the stator form a cooling duct through which coolant is pumped.
While there are a variety of techniques that may be used to cool an electric vehicle's motor, these techniques typically only provide limited heat withdrawal. Accordingly, what is needed is an effective cooling system that may be used with the high power density, compact electric motors that are commonly used in high performance electric vehicles. The present invention provides such a cooling system.